17.6. Classes and Objects: Inheritance

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Inheritance is one of the cornerstones of object-oriented programming (OOP), and it's a crucial concept to understand if you want to learn to program effectively. In the context of programming, inheritance allows programmers to create classes that are constructed from other existing classes. This allows programmers to create more specific classes that reuse, extend, and modify behavior defined in superclasses.

To better understand inheritance, let's start with a simple example. Suppose we have a class called 'Animal'. This class has attributes common to all animals, such as 'name', 'age' and 'weight', and methods such as 'eat' and 'sleep'. Now we want to create a new 'Dog' class. A dog is a type of animal, so it makes sense that the 'Dog' class inherits from the 'Animal' class. This means that the 'Dog' class will have all the attributes and methods of the 'Animal' class, plus any additional attributes and methods we define specifically for 'Dog'. For example, we can add a 'bark' method that is specific to dogs.

In terms of syntax, inheritance is usually expressed using a keyword like 'extends' or 'inherits'. For example, in Java, you could define the class 'Dog' as a subclass of 'Animal' as follows: 'public class Dog extends Animal {...}'. This means that 'Dog' is a subclass of 'Animal', and 'Animal' is the superclass of 'Dog'.

Inheritance allows programmers to reuse code efficiently. If several classes share common attributes and methods, those attributes and methods can be defined in a superclass, and subclasses can simply inherit those attributes and methods. This reduces code duplication and makes the code easier to maintain.

In addition, inheritance allows programmers to create class hierarchies that reflect the real-world relationships between different types of objects. For example, you might have a superclass 'Vehicle' with subclasses like 'Car', 'Motorbike' and 'Truck'. Each of these subclasses can have its own subclasses. For example, 'Car' can have subclasses like 'Sedan', 'Hatchback' and 'SUV'.

It is important to note that inheritance is an "is a" relationship. A 'Dog' is an 'Animal', a 'Car' is a 'Vehicle'. This is different from composition, which is a "has a" relationship. For example, a 'Car' has an 'Engine'.

In summary, inheritance is a fundamental concept in object-oriented programming that allows programmers to create classes that reuse, extend, and modify behavior defined in other classes. Inheritance increases code efficiency, reduces code duplication, and allows programmers to model real-world relationships between different types of objects.

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5117.7. Classes and Objects: Polymorphism